CASE STUDIES

Map room on the first floor. Glass in large map table allows light to penetrate through to the lobby on the ground level. High clerestory windows ring the room. Photo: Jim Schafer

Project: Cambria Office Facility

Owner: Commonwealth of Pennsylvania

Architect: L. Robert Kimbal & Associates

Mechanical Engineer: Beardsley Design Associates

Sustainable Design Consultant: Energy Opportunities, Inc.

Sustainable Materials Consultant: Horst, Inc.

CASE STUDY FEATURES:
Orientation
Daylighting
Glare
Light Shelves

 

Wood (aluminum-clad) awning windows:
triple insulating low-E glass, argon
U-factor=0.26
SHGC=0.27
VT=0.44

Wood (aluminum-clad) fixed windows:
triple insulating low-E glass, argon
U-factor=0.24
SHGC=0.27
VT=0.44

Storefront windows:
U-factor=0.26
SHGC=0.33
VT=0.49

Cambria Office Facility

Buildings and occupants rely ever more on mechanical services. Traditionally, a building's basic structure accounted for about 80% of its costs. With the transition to skeleton frame structures over the last hundred years—as opposed to load-bearing masonry—that cost has fallen to some 20%. On the other hand, the cost of building services has ballooned, with mechanical systems typically consuming 35% of the building budget. Today, more is spent on services than on any other building component.

We place tremendous importance on environmental comfort, leading to these profound changes within building expenditures. But these broad distinctions between costs for a building's basic structure and mechanical services do not sufficiently address the interplay between building components. Structure, which encompasses envelope, impacts services. For instance, consider Pennsylvania's Cambria Office Facility in Ebensburg, where investment in a high-performance, triple-glazed window system eliminates the need for perimeter heating—reducing mechanical system first costs, to say nothing of operational energy.

The Cambria project is an internally load-dominated building. It is cooled year round, even in Pennsylvania's harsh winters. Despite this, perimeter heating in this and similar buildings is invariably needed to temper the cold surface of typical glazing assemblies. Instead of perimeter heating, however, the Cambria design team addressed this issue with triple-pane windows. Triple glazing cost about $15,000 more than double-glazed windows. However, with triple glazing, a perimeter heating system, priced out at $25,000, was not needed.

South elevation of the Cambria Office Facility. Photo: Jim Schafer

The project, a 34,500-square-foot facility, constructed for and leased by the Commonwealth of Pennsylvania, was designed utilizing a systems-integration process to minimize redundancies and maximize efficiencies. The end result is that systems, like perimeter heating, were entirely eliminated or downsized. Beyond this, the triple glazing had other advantages:

  • The project air-conditioning system was reduced from 120 to 60 tons, saving $40,000. A tight, well-insulated building envelope, attention to daylighting, and other factors contributed to these savings. But project engineers and architects calculate that about 25% of this reduction—15 tons or $10,000—is attributable simply to better, more energy-efficient windows. The triple glazing saved capital costs associated with the HVAC system.
  • Regarding comfort, the standards for this building require that the interior surface temperature of the windows remain 62 degrees Fahrenheit or higher when the exterior temperature is 20 degrees Fahrenheit. Triple-glazed windows meet this requirement. Though not a prime issue with this project, triple glazing is also very resistant to sound infiltration. Triple glazing also limits condensation. With their warmer surface temperatures, less moisture forms on triple-glazed windows.

Glazing innovations and shading or light redirection elements can reduce electric lighting needs and their associated mechanical loads. However, daylight never totally supplants electric lighting; rather, the glazing and envelope help daylight complement the electric lighting. Lighting fixtures are needed when there is insufficient daylight or for night occupation. The Cambria project illustrates that triple glazing can eliminate a building component, in this case perimeter heating, thus reducing capital as well as operational costs.

South elevation with exterior light shelves on the ground level. Overhangs help control light on the first floor. Photo: Jim Schafer

Daylight is directed to the ceiling from the reflective surface in the light shelves. There is no electric lighting in these elements. The light shelf side and front "wings" block direct sunlight early in the morning and late in the afternoon at certain times of the year. Photo: Jim Schafer

The Cambria project also illustrates designers using triple glazing in concert with traditional daylighting strategies, to achieve energy consumption goals. The project is oriented longitudinally along an east-west axis, to maximize south and north exposures. Light shelves on the south-facing windows provide shade and reflect light inside, with an ultra-reflective ceiling driving daylight into the building. Roof overhangs shade second-floor south-facing windows to reduce cooling loads. Clerestory windows over the center of the second floor provide daylight from two directions, which increases daylight and distributes it more evenly to reduce glare.

The integrated manner in which the project team addressed envelope, daylight, and other issues led to Cambria's LEED Gold certification. The building uses about half the energy of similar facilities, yet it was constructed for approximately $90 per square foot, well within the cost range of conventionally constructed office buildings in the area.

Source:
Carmody, J. S. Selkowitz, E. Lee, D. Arasteh, T. Willmert. Window Systems for High-performance Buildings. Norton, 2004.

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